FPGA Optimization Guide for Intel® oneAPI Toolkits

Developer Guide

Contents

Modify the Rounding Mode of Floating-point Operations (
-Xsrounding=<rounding_type>
)

To modify the rounding mode of floating-point elementary operations in your design, use the
-Xsrounding=
<rounding_type>
 option in your
dpcpp
 command. You can set the
-Xsrounding
 option to one of the following values:
  • ieee
    : All elementary operations (
    +
    ,
    -
    ,
    *
    ,
    /
    ) of both single-precision and double-precision floating-point use IEEE-754 round nearest ties to even (RNE) mode, which has a 0.5 unit of least precision (ULP) error at most.
  • faithful
    : All elementary operations of double-precision floating-point and multiplication and division of single-precision floating-point use faithful rounding mode, which has a 1 ULP error at most. This rounding mode leads to more efficient hardware at the expense of numerical variation in results. Addition and subtraction of single-precision floating-point still have to use IEEE-754 RNE rounding mode.
The following tables summarize the rounding modes:

Single-precision Floating-point

Addition
Subtraction
Multiplication
Division
Default
IEEE-754 RNE
IEEE-754 RNE
IEEE-754 RNE
Faithful
-Xsrounding=ieee
IEEE-754 RNE
IEEE-754 RNE
IEEE-754 RNE
IEEE-754 RNE
-Xsrounding=faithful
IEEE-754 RNE
IEEE-754 RNE
Faithful
Faithful

Double-precision Floating-point

Addition
Substraction
Multiplication
Division
Default
IEEE-754 RNE
IEEE-754 RNE
IEEE-754 RNE
IEEE-754 RNE
-Xsrounding=ieee
IEEE-754 RNE
IEEE-754 RNE
IEEE-754 RNE
IEEE-754 RNE
-Xsrounding=faithful
Faithful
Faithful
Faithful
Faithful
Examples
dpcpp -fintelfpga -Xshardware -Xsrounding=ieee <source_file>.cpp
dpcpp -fintelfpga -Xshardware -Xsrounding=faithful <source_file>.cpp

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.